System and method that dissipate heat from an electronic device

ABSTRACT

The electronic system includes an electronic device and a liquid holding section that is thermally coupled to the electronic device. The electronic system further includes an impermeable section that engages the liquid holding section. The impermeable section includes a channel and a plurality of passages that provide fluid communication between the liquid holding section and the channel. The electronic system further includes (i) a first fluid that flows through the channel in the impermeable section to facilitate heat transfer from the electronic device to the first fluid; and (ii) a second fluid that flows from the liquid holding section through the plurality of passages into the channel when the second fluid boils within the liquid holding section due to heat transfer from the electronic device to the second fluid. In some embodiments, the first and second fluids are different types of substances.

BACKGROUND

The present invention relates generally to the field of electronicdevices, and in particular to the thermal management of high-poweredelectronic devices.

Electronic devices generate heat during operation. Thermal managementrefers to the ability to keep temperature-sensitive elements in anelectronic device within a prescribed operating temperature. Thermalmanagement has continually evolved to address the increased heatgeneration created within such electronic devices as a result of theincreased processing speed/power that is usually associated with eachnew generation of electronic devices.

Historically, electronic devices were cooled by a natural convectionthermal management technique. The cases or packaging of these prior artelectronic devices were designed with openings (e.g., slots)strategically located to allow warm air to escape and cooler air to bedrawn in.

The advent of high performance electronic devices now requires moreinnovative thermal management. Each increase in processing speed andpower generally carries a “cost” of increased heat generation such thatnatural convection is no longer sufficient to provide proper thermalmanagement.

Several methods have been employed for cooling high performanceelectronic devices. One common method of cooling an electronic deviceincludes attaching one or more heat sinks to the electronic device. Aheat sink is typically used in combination with a fan that forces air topass by the heat sink and/or the electronic device.

There are several problems with cooling systems that utilize some formof a heat sink and fan combination. One problem is that more air flow isgenerally needed in order adequately dissipate heat from the electronicdevice. This increase in air flow is typically generated by a larger fanand/or increased fan speed which can result in unwanted acoustic noise.Another problem is that the fan must typically be located too closely tothe fins of the heat sink to generate fully developed air flow. Inaddition, when a large fan is used in conjunction with a heat sink tocool an electronic component, a large percentage of the air moved by thesystem fan does not go through the heat sink. As a result, even largefans are not a sufficient thermal solution for cooling some electronicdevices.

An alternative and more costly system to manage the thermal energyoutput of high-powered electronic devices is a liquid cooling system.Most liquid cooling systems include a heat exchanger that is thermallyconnected to the electronic device.

A relatively recent trend has seen the use of “two-phase” coolingsystems to cool high-powered electronic devices. These two phase coolingsystems include an evaporator or flow channels that remove thermalenergy from the electronic device. The thermal energy causes a coolantwithin the evaporator or flow channels to turn from a liquid into avapor (i.e., to evaporate) or vapor-liquid mixture.

These “two-phase” cooling systems suffer from several drawbacks. Onedrawback is that the systems require the use of a pump. These pumpsrequire maintenance and commonly break down or leak onto one or more ofthe electrical components. Another drawback is that many electronicdevices are now putting out so much thermal energy that existingtwo-phase cooling systems often have trouble thermally managingelectronic devices under more extreme operating conditions.

Since many electronic systems are not able to effectively cool the highperformance electronic devices that are within such systems undercertain operating conditions, an electronic system is needed thatprovides superior cooling to high-powered electronic devices under avariety of operating conditions.

SUMMARY

Some example embodiments of the present invention relate to anelectronic system that includes an electronic device and a liquidholding section that is thermally coupled to the electronic device. Theelectronic system further includes an impermeable section that engagesthe liquid holding section. The impermeable section includes a channeland a plurality of passages that provide fluid communication between theliquid holding section and the channel.

The electronic system further includes (i) a first fluid that flowsthrough the channel in the impermeable section to facilitate heattransfer from the electronic device to the first fluid; and (ii) asecond fluid that flows from the liquid holding section through theplurality of passages into the channel when the second fluid boilswithin the liquid holding section due to heat transfer from theelectronic device to the second fluid. In some embodiments, the firstfluid is one type of substance (e.g., water) and the second fluid is adifferent type of substance (e.g., FC-72).

As the second fluid emerges from each of the passages, the second fluidmixes with the first fluid such that the flow within the channel becomesmore turbulent. This more turbulent flow within the channel increasesthe capacity of the first and second fluids to transfer heat from theelectronic device.

In some embodiments, the method may further include opening one or morevalves that prevent the flow of the second fluid from the passages intothe channel. It should be noted that opening one or more the valves mayinclude (i) raising the temperature of the valves to a certain level;and/or (ii) exposing the valves to a pressure within the passages thatis sufficient to open the valves.

Other example embodiments of the present invention relate to a method ofcooling an electronic device. The method includes transferring heat fromthe electronic device to a first fluid that flows through a channel inan impermeable section. The method further includes transferring heatfrom the electronic device to a liquid holding section that includes asecond fluid. The heat is transferred to the second fluid until thesecond fluid boils and passes through a plurality of passages in theimpermeable section into the channel in the impermeable section. In someembodiments, the first and second fluids are different substances suchthat the method further includes separating the first fluid from thesecond fluid once the first and second fluids exit the channel in theimpermeable section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an example electronic system.

FIG. 2 is an enlarged schematic side view illustrating a portion ofanother example embodiment of the electronic system shown in FIG. 1.

FIG. 3 is an enlarged schematic side view similar to FIG. 2 illustratinga portion of another example embodiment of the electronic system shownin FIG. 1.

FIG. 4 is a schematic side view of an example electronic system thatincludes a plurality of closed valves.

FIG. 5 is a schematic side view of the example electronic system shownin FIG. 4 with some of the valves open.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof, and in which is shown by way ofillustration specific embodiments which may be practiced. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be utilized and that structural, logical andelectrical changes may be made without departing from the scope of thepresent invention. The following description is, therefore, not to betaken in a limited sense, and the scope of the present invention isdefined by the appended claims.

FIG. 1 illustrates an example electronic system 10. The electronicsystem 10 includes an electronic device 12 and a liquid holding section14 that is thermally coupled to the electronic device 12.

The electronic system 10 further includes an impermeable section 16 thatengages the liquid holding section 14. The impermeable section 16includes a channel 18 and a plurality of passages 20 that provide fluidcommunication between the liquid holding section 14 and the channel 18.In some embodiments, the electronic system 10 may further include aninterface 13 that facilitates transferring heat (identified as H in theFIGS.) from the electronic device 12 to the liquid holding section 14.

During operation of the electronic system 10 a first fluid 22 flowsthrough the channel 18 in the impermeable section 16 to facilitate heattransfer from the electronic device 12 to the first fluid 22. Inaddition, a second fluid 24 flows from the liquid holding section 14through the plurality of passages 20 into the channel 18 when the secondfluid 24 boils within the liquid holding section 14 due to heat transferfrom the electronic device 12 to the second fluid 24. As shown in theFIGS., the electronic device 12 may generate localized “hot spots”during operation so that differing amounts of heat may be transferred tothe liquid holding section 14 from the electronic device 12 depending onthe design of the electronic device 12.

In some embodiments, the first fluid 22 and the second fluid 24 are thesame substance while in other embodiments the first fluid 22 and thesecond fluid 24 are different substances. As an example, the first fluid22 may be water and the second fluid 24 may be FC-72.

It should be noted that in those embodiments where the first and secondfluids 22, 24 are different substances, the electronic system 10 mayfurther include a separator 26 that separates the first fluid 22 fromthe second fluid 24 after the first and second fluids 22, 24 exit thechannel 18. In addition, the electronic system 10 may further include apump 28 that forces the first fluid 22 to flow through the channel 18 inthe impermeable section 16.

In some embodiments, the liquid holding section 14 spreads the secondfluid 24 throughout the liquid holding section 14 via capillary actionthat takes place within the liquid holding section 14. The manner inwhich the second fluid 24 is brought into contact with the liquidholding section 16 will depend in part on the overall configuration ofthe electronic system 10.

One example material for the liquid holding section 14 is porous siliconwhile an example material for the impermeable section 16 is silicon. Inaddition, the passages 20 in the impermeable section 16 may range fromabout 1 to 300 square μm in cross-section size while the channel 18 inthe impermeable section 16 may range from about 20 to 1000 square μm incross-section size (although other cross-section sizes are possible).

In the example embodiment that is illustrated in FIG. 1, the first fluid22 flows through the channel 18 in a first direction F and the secondfluid 24 initially flows from the plurality of passages 20 into thechannel 18 in a second direction D1 which is orthogonal to the firstdirection F. FIG. 2 illustrates an example embodiment where the secondfluid 24 initially flows from the plurality of passages 20 into thechannel 18 in a second direction D2 that is at least partially the sameas the first direction F. FIG. 3 illustrates an example embodiment wherethe second fluid 24 initially flows from the plurality of passages 20into the channel 18 in a second direction D3 that is at least partiallyopposite to the first direction F.

As the second fluid 24 emerges from each of the passages 20, the secondfluid 24 mixes with the first fluid 22 such that the flow of fluidwithin the channel 18 becomes more turbulent. This more turbulent flowincreases the capacity of the first and second fluids 22, 24 to transferheat from the electronic device 12.

In the example embodiment that is illustrated in FIG. 2, the secondfluid 24 may provide a sufficient force to move the first and secondfluids 22, 24 through the channel 18 in direction F without the use of apump. Eliminating or reducing the need to use of a pump to drive thefirst and/or second fluids 22, 24 through the channel 18 would remove orminimize many of the drawbacks that are associated with using a pump aspart of an electronic system 10.

Although the second fluid 24 is shown in each of the FIGS. 1-3 asexiting from each of the passages 20 in the same direction, some of thepassages 20 may direct the second fluid 24 into the channel 18 indifferent directions. In addition, it should be noted that while FIG. 1appears to show that the second fluid 24 enters the channel 18 from onlyabove and below the channel 18, the second fluid 24 may enter thechannel 18 from any orientation (i.e., above, below and/or sides), orany combination of orientations. The orientation (or orientations) fromwhich the second fluid 24 enters the channel 18 will depend in part onthe overall design of the electronic system 10.

In the example embodiment that is illustrated in FIG. 1, the liquidholding section 14 is formed of two layers 15A, 15B. It should be notedthat the number and arrangement of the layers that form the liquidholding section 14 and the impermeable section 16 will depend in part onthe overall configuration of the electronic system 10 as well asmanufacturing considerations related to fabricating the electronicsystem 10.

In addition, the impermeable section 16 may include multiple channels18. The number of layers and/or channels 18 will depend in part on thesize of the electronic device 12 and the cooling requirements of theelectronic device 12.

FIGS. 4-5 illustrate an example embodiment of the electronic system 10where the electronic system 10 includes a plurality of valves 30. Asshown in FIG. 4, each of the plurality of valves 30 prevents the secondfluid 24 from leaving a passage 20. In some embodiments, the valves 30prevent the second fluid 24 from leaving a respective passage 20 until(i) each respective valve 30 reaches a desired temperature; and/or (ii)the pressure within each respective passage 20 reaches a desired level.The temperature and/or pressure levels that would be required to openeach valve 30 may be determined in part by the material that is selectedfor each valve 30 and the size of each valve 30.

Some example materials for the valves 30 include a shape memory alloy(SMA). Some SMA's are a metal that “remembers” its geometry. Someexample types of SMAs include copper-zinc-aluminium,copper-aluminium-nickel, and nickel-titanium (NiTi) alloys. NiTi alloysare generally more expensive and possess superior mechanical propertieswhen compared to copper-based SMAs.

In some embodiments, the passages 20 may be designed with a particularsize and/or shape to establish the desired pressure that would berequired to open the valves 30. FIGS. 4 and 5 illustrate an exampleembodiment where one of passages 20 includes a reservoir 32 (see passage20 that is farthest to the right in FIGS. 4 and 5) that allows thepressure to build up within the passage 20 before the correspondingvalve 30 opens. Although only one reservoir 32 is shown in FIGS. 4 and5, any number of passages 20 may include reservoirs of varying sizes andshapes. It should be noted that each of the valves 30 may be designed toopen at different pressure and/or temperature levels.

Other example embodiments relate to a method of cooling an electronicdevice 12. The method includes transferring heat from the electronicdevice 12 to a first fluid 22 that flows through a channel 18 in animpermeable section 16. The method further includes transferring heatfrom the electronic device 12 to a liquid holding section 16 thatincludes a second fluid 24 until the second fluid 24 boils and passesthrough a plurality of passages 20 in the impermeable section 16 intothe channel 18 in the impermeable section 16.

The method may further include pumping the first fluid 22 through thechannel 18 in the impermeable section 16 (see, e.g., pump 28 in FIG. 1).In addition, when the first and second fluids 22, 24 are differentsubstances, the method may further include separating the first fluid 22from the second fluid 24 once the first and second fluids 22, 24 exitthe channel 18 in the impermeable section 16 (see, e.g., separator 26 inFIG. 1).

In some embodiments, transferring heat from the electronic device 12 tothe liquid holding section 14 until the second fluid 24 boils mayinclude ejecting the second fluid 24 from the plurality of passages 20into the channel 18 in a direction that is orthogonal to the flow of thefirst fluid 22 within the channel 18 (see, e.g., FIG. 1). In otherembodiments, transferring heat from the electronic device 12 to theliquid holding section 14 until the second fluid 24 boils may includeejecting the second fluid 24 from the plurality of passages 20 into thechannel 18 in a direction that is partially the same as the flow of thefirst fluid 22 within the channel 18 (see, e.g., FIG. 2). It should benoted that embodiments are contemplated that include ejecting the secondfluid 24 into the channel 18 in multiple directions and/or from multipleorientations.

The method may further include opening one or more valves 30 thatprevent the flow of the second fluid 24 from the passages 20 into thechannel 18. It should be noted the valves 30 may be opened and closed inany manner. As examples, opening one or more of the valves 30 mayinclude (i) raising the temperature of the valves 30 to a certain level;and/or (ii) exposing the valves 30 to a pressure within the passages 20that is sufficient to open the valves 30.

The electronic systems and methods described herein may be implementedutilizing a number of different types of electronic devices. Theelements, materials, geometries, dimensions, and sequence of operationscan all be varied to suit particular requirements.

FIGS. 1-5 are merely representational and are not drawn to scale.Certain proportions thereof may be exaggerated while others may beminimized.

The electronic systems and methods described above may provide a thermalsolution for cooling high powered electronic devices. Many otherembodiments will be apparent to those of skill in the art from the abovedescription.

The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow thereader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

1. An electronic system comprising: an electronic device; a liquidholding section thermally coupled to the electronic device; animpermeable section engaging the liquid holding section such that theliquid holding section is sandwiched between the impermeable section andthe electronic device, the impermeable section including a channel and aplurality of passages that provide fluid communication between theliquid holding section and the channel; a first fluid that flows throughthe channel in the impermeable section to facilitate heat transfer fromthe electronic device to the first fluid; and a second fluid that flowsfrom the liquid holding section through the plurality of passages intothe channel when the second fluid boils within the liquid holdingsection due to heat transfer from the electronic device to the secondfluid, wherein the first fluid is one type of substance and the secondfluid is a different type of substance.
 2. The electronic system ofclaim 1 wherein the first fluid is water and the second fluid is FC-72.3. The electronic system of claim 2 further comprising a separator thatseparates the water from the FC-72 after the first and second fluidsexit the channel.
 4. The electronic system of claim 1 wherein the firstfluid flows through the channel in a first direction and the secondfluid initially flows from the plurality of passages into the channel ina second direction which is orthogonal to the first direction.
 5. Theelectronic system of claim 1 wherein the first fluid flows through thechannel in a first direction and the second fluid initially flows fromthe plurality of passages into the channel in a second direction that isat least partially the same as the first direction.
 6. The electronicsystem of claim 1 wherein the first fluid flows through the channel in afirst direction and the second fluid initially flows from the pluralityof passages into the channel in a second direction that is at leastpartially opposite to the first direction.
 7. The electronic system ofclaim 1 further comprising a pump that forces the first fluid to flowthrough the channel in the impermeable section.
 8. The electronic systemof claim 1 wherein the liquid holding section spreads the second fluidthroughout the liquid holding section via capillary action within theliquid holding section.
 9. The electronic system of claim 1 wherein thesecond fluid initially flows from the each of the passages into thechannel in the same direction.
 10. The electronic system of claim 1wherein the liquid holding section is formed of two layers.
 11. Theelectronic system of claim 1 wherein the liquid holding section isformed of a porous material.
 12. The electronic system of claim 11wherein the liquid holding section is porous silicon.
 13. The electronicsystem of claim 1 further comprising a plurality of valves where eachvalve prevents fluid from exiting a corresponding one of the passages.14. The electronic system of claim 13 wherein each valve prevents fluidfrom exiting a corresponding one of the passages until the valve reachesa desired temperature.
 15. The electronic system of claim 13 whereineach valve prevents fluid from exiting a corresponding one of thepassages until the pressure within the respective passage reaches adesired level.